It is well-known that many plants are sensitive to drops in temperature, even above the freezing point. This is the case for most fruit-bearing trees.
It has been determined that frost and other fluctuations in temperature, including dryness and excessive heat, are aggressive to plant life, generating a phenomenon defined as xe2x80x9coxidative stressxe2x80x9d, defined as an accelerated and excessive generation of free radicals: alkoxy, peroxy, and oxygen singlets. These free radicals are produced by the interaction of lipooxygenase with the lipids of cell membranes.
In the case of excessive dryness, the formation of super-oxidated anions (O2xc2x0) among the plant chloroplasts has been observed.
This oxidative stress leads to the formation of derivatives toxic to living cells such as malondialdehyde (MDA), this last substance being an indicator of the level of oxidative deterioration. Lipoperoxidation is indicated by the reaction of thiobarbituric acid with MDA.
The accumulation of lipoperoxides provokes an activation of the senescence of the leaves and dicotyledons.
It has been determined that the senescent leaves and dicotyledons accumulated fluorescent substances are derived from the oxidative process of unsaturated fatty acids. These fluorescent substances are also the end products of peroxidation, obtained by the interaction of aldehydic functions, particularly that of MDA upon the amino function of the proteins.
This oxidative stress provokes a decrease in superoxide dismutase (SOD), as well as a perturbation of membranoid proteins, as we have observed notably in vegetables.
The degenerative activity of lipid peroxidation is evident not only for plants at various stages of growth but also during the period of seed germination, according to the levels of hydroperoxidation present.
Many plants are rich in polyphenols (flavonoids) which are powerful antioxidants. The levels of these polyphenols are more elevated in plants in sunlight than in those located in the shade.
The present invention is intended to protect plants against the aforementioned oxidative stress with the use of compounds of lipo-amino acids specifically selected for their capacity as antioxidants.
Compounds of lipo-amino acids have been previously described as active agents for the stimulation of vegetal biosynthesis, or as fertilizing agents. These structures have also been cited as having antibacterial and antifungal properties in the following patents: FR-A-2 403 024, FR-A-2 503 153, FR-A-2 503 144.
The French patent FR-A-2 503 151 also mentions sulpho-butyryl-amino acids such as methionine or cystine but not in relation to any protection against lipoperoxidation. It is only recently that the antioxidant properties of butyryl-methionine have been discovered; butyryl-cystine, on the other hand, does not possess these properties.
French patent FR-A-85 137 38 concerns the utilization of lipo-amino acids and their salts to increase floral fertility. It is also a highly specified process.
French patent FR-A-2 503 153 concerns lipo-amino acids of proline and hydroxyproline which have specific effects upon dryness in plant life.
Later studies upon lipo-amino acids of proline have shown that those compounds also protected against the adverse effects of frost.